At the end of the road along the Grand Canyon's South Rim, past Hermits Rest, a famous rock cabin built in 1914 that's now a rustic souvenir and snack shop, there's an inviting rock outcropping where you can stretch out in solitude and gaze across the canyon.

On a late April afternoon, no one else approaches for more than an hour. Sitting still, eyes closed, you begin to notice the subtle sounds of nature -- the grasses rustling in the breeze, the flap of wings as a swift darts after insects. Yet the sense of refuge is fragile and easily broken, because the sound of machinery intrudes: Helicopters. One or two, sometimes as many six, can be seen at any given moment in the sky to the west. They carry a different kind of tourist, and their cacophony echoes off the canyon walls and bounces down the Hermit Trail.

The conflict -- airborne tours versus on-the-ground visitors, including backpackers and river-runners who come to the park for a more natural experience -- continues 24 years after Congress attempted a solution with the 1987 National Parks Overflights Act.

The law was largely intended to improve the safety of canyon flights, after a 1986 collision of a tour airplane and a tour helicopter killed 25 people. But it also called for the National Park Service's parent agency, the Department of Interior, to work with the Federal Aviation Administration for a "substantial restoration of the natural quiet and experience of the park."

There has been some progress. In the Wild West era of the mid-1980s, tour helicopters often flew below the rim, hovering close to waterfalls and other backcountry destinations popular with hikers. The law eliminated below-the-rim tour flights, except for those landing on the Hualapai Tribe's property outside the park's boundaries, and established flight corridors -- like the one a few miles west of Hermits Rest -- in order to reduce conflicts.

But the law left many details undefined and set off a wrestling match between the Park Service and the FAA, whose mission is to promote air traffic. The FAA has issued a series of regulations, and the Park Service has frequently weighed in with recommendations. The Department of Transportation, which includes the FAA, and the Department of Interior eventually agreed that the Park Service can make the noise regulations, and the FAA will ensure they're implemented safely. Researchers have measured the noise and used computer models to study how to alleviate it. The air-tour industry sued the FAA and the Park Service, trying to weaken the regulations, and environmental groups -- including the Grand Canyon Trust, National Parks Conservation Association and the Sierra Club -- have gone to court seeking to toughen them.

Meanwhile, the traffic increased to more than 80,000 annual flights in the late 1990s, then declined to around 48,000-57,000 annual flights in recent years, largely due to economic factors. (The FAA allows up to 93,971 air-tour flights per year in the park.) Congress has also urged the agencies to create incentives for aircraft to adopt "quiet technology," such as shrouds on helicopter rotors, as a provision of the 2000 National Parks Air Tour Management Act. Some are using such technology, but incentives remain few and there's no requirement. Environmentalists scoff at the term "quiet technology." It just means "less noisy," says Roger Clark, a former river guide who works for the Grand Canyon Trust.

The long wrestling match is coming to a head. In February, the National Park Service released a draft environmental impact statement that lays out options for reducing noise; the public can submit comments until June 20.

The Park Service's "preferred alternative" would allow up to 65,000 tour flights per year and require aircraft to adopt quieter technology within 10 years. No flights would be allowed in the first hour after sunrise and the last hour before sunset. Some flight corridors would be shifted "to better protect" areas where hikers and river runners particularly desire quiet, such as Hermits Rest and the river's Marble Canyon stretch. Two popular flight corridors would be closed for half of each year, to offer people on the ground guaranteed quiet. The Park Service says that all the changes would restore "natural quiet" to 67 percent of the 1.2 million-acre park, compared to 53 percent these days.

Every time regulations are proposed, the air-tour industry predicts economic disaster, and the DEIS is no exception. Steve Bassett, head of the U.S. Air Tour Association, says the Park Service's proposal is "designed to drive the industry out of existence in the Grand Canyon."

Elling Halvorson, the leading air-tour provider, says the 277-mile-long canyon has roads along only 30 miles of the rims, and "everyone would like to see the canyon from the air" because it's "a totally different experience."

The industry has considerable political clout, and connections with the huge casino resorts in Las Vegas, Nev. The air-tour companies use bases in Las Vegas and send shuttles and limousines to the casino resorts to pick up customers, and the resorts steer their guests to the flights, describing them as another way to have a good time in Vegas. The casino resorts and hotels have contributed more than $2 million to Nev. Sen. Harry Reid's campaigns since the 1980s, and Reid has tried to block tougher regulations in recent years; they've also been significant backers of Ariz. Sen. John McCain and other supportive congressmen.

McCain has flip-flopped: He co-sponsored the 1987 law, saying, "When it comes to a choice between the interests of our parks system, and those who profit from it, without a doubt the interests of the land must come first." But since then, he's become a leading advocate for the air-tour industry.

"It is important that we restore quiet (in) Grand Canyon National Park," McCain said in a March 2010 Senate speech introducing a pro-industry measure (which was defeated). "At the same time, it is also very important that people from all over the world have the opportunity to enjoy one of the great and magnificent experiences that any person can have -- that is to view the Grand Canyon from the air as well as from the ground."

Environmentalists want tougher limits than the Park Service's preferred alternative would impose. Clark says the agency "crafted a political compromise" in the hopes that both camps would "hold their noses and say, 'OK, we can live with it.' " The preferred alternative offers the industry "regulatory certainty" after years of upheaval, he points out. But he adds that the industry is still applying political pressure to further swing the balance in its favor as the Park Service and FAA evaluate comments and reach a final decision.

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